This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
Various abbreviations that may appear in the specification and/or in the drawing figures are defined as follows:                3GPP third generation partnership project        ACK acknowledge        AN ACK/NACK        CCE control channel element        CQI channel quality indicator        DAI downlink activity indicator        DL downlink (eNB towards UE)        eNB EUTRAN Node B (evolved Node B)        EPC evolved packet core        EUTRAN evolved UTRAN (LTE)        FDD frequency division duplex        FDMA frequency division multiple access        HARQ hybrid automatic repeat request        LTE long term evolution        MAC medium access control        MM mobility management        MME mobility management entity        NACK not (negative) acknowledge        Node B base station        O&M operations and maintenance        OFDMA orthogonal frequency division multiple access        PCFICH physical control format indicator channel        PDCP packet data convergence protocol        PHY physical        PRB physical resource block (180 kHz)        PUCCH physical uplink control channel        PUSCH physical uplink shared channel        RB resource block        RLC radio link control        RRC radio resource control        RRM radio resource management        SC-FDMA single carrier, frequency division multiple access        S-GW serving gateway        TDD time division duplex        UE user equipment        UL uplink (UE towards eNB)        UTRAN universal terrestrial radio access network        
A communication system known as evolved UTRAN (E-UTRAN, also referred to as UTRAN-LTE or as E-UTRA) is currently under development within the 3GPP. As presently specified the DL access technique will be OFDMA, and the UL access technique will be SC-FDMA.
One specification of interest is 3GPP TS 36.300, V8.4.0 (2008-03), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Access Network (E-UTRAN); Overall description; Stage 2 (Release 8). One section of particular relevance to the ensuing discussion is Section 5.2, Uplink Transmission Scheme.
FIG. 1 reproduces FIG. 4.1 of 3GPP TS 36.300, and shows the overall architecture of the E-UTRAN system. The E-UTRAN system includes eNBs, providing the E-UTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the UE (not shown). The eNBs are interconnected with each other by means of an X2 interface. The eNBs are also connected by means of an S1 interface to an EPC, more specifically to a MME (Mobility Management Entity) by means of a S1 MME interface and to a Serving Gateway (SGW) by means of a S1 interface. The S1 interface supports a many-to-many relationship between MMEs/S-GW and eNBs.
The eNB hosts the following functions:
functions for Radio Resource Management: Radio Bearer Control, Radio Admission Control, Connection Mobility Control, Dynamic allocation of resources to UEs in both uplink and downlink (scheduling);
IP header compression and encryption of user data stream;
selection of a MME at UE attachment;
routing of User Plane data towards Serving Gateway;
scheduling and transmission of paging messages (originated from the MME);
scheduling and transmission of broadcast information (originated from the MME or O&M); and
measurement and measurement reporting configuration for mobility and scheduling.
Also of interest herein are the Layer 1 (PHY) specifications, such as those found in 3GPP TS 36.211 V8.2.0 (2008-03), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8), as well as 3GPP TS 36.213 V8.3.0 (2008-05), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Layer Procedures (Release 8).
Two different approaches have been discussed in 3GPP regarding the ACK/NACK signaling in TDD mode. A first approach can be referred to as ACK/NACK bundling (bundled-AN), where ACK/NACK feedback related to multiple DL sub-frames is compressed into a single ACK/NACK feedback transmitted via a single ACK/NACK resource. A second approach can be referred to as multi-ACK/NACK (multi-AN), where each DL subframe is considered as a separate HARQ process, and where a separate ACK/NACK feedback is transmitted for each (granted) DL subframe.
Of particular interest herein is the ACK/NACK bundling approach.
In R1-081110, “Multiple ACK/NACK for TDD”, Ericsson, Motorola, Nokia, Nokia Siemens Networks, Qualcomm, it was agreed that DL hybrid ARQ (HARQ) acknowledgments in TDD can be transmitted as a single ACK/NACK feedback, where ACK/NACKs from one or several DL subframes are combined (“bundled” by performing an AND operation of all ANs) to a single ACK/NACK report. The PUCCH formats already defined for LTE are reused (PUCCH Format 1a/1b). This ACK/NACK mode has been referred to as “ACK/NACK-bundling” or more simply as “AN-bundling”.
In R1-082168 and R1-082100, “ACK/NACK Bundling for TDD: Way Forward”, Motorola, CATT, CMCC, Ericsson, Huawei, LGE, Qualcomm, Samsung, Texas Instruments, it was agreed regarding AN bundling for UL/DL configurations (except configuration 5) that a 2-bit Downlink Assignment Index field is added to DCI formats 1, 1A, 1B, 2. The Downlink Assignment Index must be greater than or equal to the number of previously assigned subframes within the bundling window and must be less than or equal to the maximum number of dynamic assignments within the bundling window. It was also agreed that the UE uses the CCE index in a last received/detected dynamic DL assignment, as well as the subframe number, to check for missed DL assignments and to determine the UL ACK/NACK PUCCH index. It was also agreed that semi-persistent assignments are not counted in the Downlink Assignment Index.
In R1-082243, “CR for UL ACK/NACK procedure for TDD”, Motorola, it was agreed that the UE determines the UL ACK/NACK PUCCH index based on the lowest CCE index and downlink subframe number of the last received/detected dynamic assignment (the exact formula to use when determining the UL ACK/NACK PUCCH index was left for future study).
AN bundling is used when there are more downlink subframes than uplink subframes per radio frame. With the agreements made thus far in 3GPP RAN1, each downlink subframe will have its unique PUCCH AN resources in association therewith, while the specified AN bundling feature will only require occupying a single PUCCH AN resource at a given time, regardless how many DL HARQ ANs have been “bundled” together. This implies that, for example, if the bundling window is 4 DL subframes, each UE will use only 1 out of the 4 reserved PUCCH AN resources, while the remaining 3 PUCCH AN resources will be unused. As can be appreciated, this approach is wasteful when UL resources are scarce. This is particularly true, given the fact that UL is already in short supply when AN-bundling is applied (DL subframes>UL subframes).
R1-081816, “CCE to bundled ACK/NACK index mapping in TDD”, LG Electronics, and R1-081788, “Uplink ACK/NACK implicit mapping in TDD”, Huawei, partially address the PUCCH resource usage, but not the over-reservation per UE issue.